Abstract The Lunar Trailblazer mission aimed to assess the presence of water on the lunar surface using imaging spectroscopy in visible shortwave infrared (VSWIR) coupled with high‐resolution multispectral imaging in thermal midwave‐infrared (MWIR), captured simultaneously over the same target from orbit around the Moon with two different instruments. Uncertainties in clock timing, instrument models, and instrument pointing knowledge manifest as geospatial offsets between the two data sets that must be corrected in post‐processing to enable co‐registration, tying the acquired images to their precise latitudes and longitudes on the Moon. This work describes an algorithmic approach to co‐registering and geolocalizing images after acquisition without high precision instrument and spacecraft pointing models, the Iterative Matching Pipeline for Post‐Acquisition Image Localization (IMPPAIL), utilizing previously acquired data for development. We use Lunar Orbiter Laser Altimetry (LOLA) and Kaguya data to make shaded relief maps as the basemap on which to project data. To test our processing pipeline prior to Lunar Trailblazer data collection, we use Moon Mineralogy Mapper (M3) data for VSWIR images and simulated MWIR images. When demonstrated on these data sets, IMPPAIL produces a 98% success rate registering VSWIR data to LOLA/Kaguya shaded relief maps and successfully co‐registered MWIR and VSWIR in all four simulation cases. We include a code package with software tools allowing this algorithm to be used for a variety of data sets across many other missions.

Impact cratering is a key process on rocky bodies in the solar system. The subsequent degradation of impact-crater walls can record ancient environmental conditions, such as surface water on Mars. Distinguishing erosional landforms associated with liquids from those associated with dry processes remains challenging. Here, we developed a model for landform development under a dry end-member case of degradation by rockfall. Unlike canonical models of crater degradation by regolith creep that smooth and relax hillslopes, results show that rockfalls produce channelized landforms. Rockfall locally oversteepens slopes, leading to increased rockfall generation, which is then funneled into topographic lows, causing chute development through topographic feedback similar to river incision. While typically neglected in landscape evolution models, rockfalls can shape crater walls and steep rocky slopes, creating channelized landforms by dry processes that are not possible with regolith creep alone.

Research Article| December 01, 2023 Lunar Mare Basaltic Volcanism: Volcanic Features and Emplacement Processes James W. Head; James W. Head Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA Search for other works by this author on: GSW Google Scholar Lionel Wilson; Lionel Wilson Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK Search for other works by this author on: GSW Google Scholar Harald Hiesinger; Harald Hiesinger Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany Search for other works by this author on: GSW Google Scholar Carolyn van der Bogert; Carolyn van der Bogert Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany Search for other works by this author on: GSW Google Scholar Yuan Chen; Yuan Chen Key Laboratory for Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, China Search for other works by this author on: GSW Google Scholar James L. Dickson; James L. Dickson Division of Geological and Planetary Science, California Institute of Technology, 1200 E California Blvd, MC 150–21. Pasadena, CA, 91125, USA Search for other works by this author on: GSW Google Scholar Lisa R. Gaddis; Lisa R. Gaddis Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, USA Search for other works by this author on: GSW Google Scholar Junichi Haruyama; Junichi Haruyama Institute of Space and Astronautical Science, JAXA, Japan (3–1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252–5210, Japan) Search for other works by this author on: GSW Google Scholar Erica R. Jawin; Erica R. Jawin Smithsonian Institution National Museum of Natural History, Department of Mineral Sciences, PO Box 37012, Washington, DC 20013–7012, USA Search for other works by this author on: GSW Google Scholar Lauren M. Jozwiak; Lauren M. Jozwiak Johns Hopkins Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD 20723, USA Search for other works by this author on: GSW Google Scholar Chunlai Li; Chunlai Li Key Laboratory for Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, China Search for other works by this author on: GSW Google Scholar Jianzhong Liu; Jianzhong Liu Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China Search for other works by this author on: GSW Google Scholar Tomokatsu Morota; Tomokatsu Morota Department of Earth and Planetary Science, University of Tokyo, Bunkyō-ku, Tokyo, Japan Search for other works by this author on: GSW Google Scholar Debra H. Needham; Debra H. Needham National Aeronautics and Space Administration Headquarters, Washington, D.C. 20546, USA Search for other works by this author on: GSW Google Scholar Lillian R. Ostrach; Lillian R. Ostrach US Geological Survey Astrogeology Science Center, 2255 N. Gemini Drive, Flagstaff, AZ USA Search for other works by this author on: GSW Google Scholar Carle M. Pieters; Carle M. Pieters Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA Search for other works by this author on: GSW Google Scholar Tabb C. Prissel; Tabb C. Prissel Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX 77058 USA Search for other works by this author on: GSW Google Scholar Yuqi Qian; Yuqi Qian Planetary Science Institute, China University of Geosciences, Wuhan, 430074, China Search for other works by this author on: GSW Google Scholar Le Qiao; Le Qiao Institute of Space Science, Shandong University, Weihai, 264209, China Search for other works by this author on: GSW Google Scholar Malcolm R. Rutherford; Malcolm R. Rutherford Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA Search for other works by this author on: GSW Google Scholar David R. Scott; David R. Scott Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA Search for other works by this author on: GSW Google Scholar Jennifer L. Whitten; Jennifer L. Whitten Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA 70118 USA Search for other works by this author on: GSW Google Scholar Long Xiao; Long Xiao Planetary Science Institute, China University of Geosciences, Wuhan, 430074, China Search for other works by this author on: GSW Google Scholar Feng Zhang; Feng Zhang National Space Science Center, No. 1 Nanertiao, Zhongguancun, Haidian District, Beijing, China Search for other works by this author on: GSW Google Scholar Ouyang Ziyuan Ouyang Ziyuan Key Laboratory for Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, China Search for other works by this author on: GSW Google Scholar Author and Article Information James W. Head Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA Lionel Wilson Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK Harald Hiesinger Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany Carolyn van der Bogert Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany Yuan Chen Key Laboratory for Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, China James L. Dickson Division of Geological and Planetary Science, California Institute of Technology, 1200 E California Blvd, MC 150–21. Pasadena, CA, 91125, USA Lisa R. Gaddis Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, USA Junichi Haruyama Institute of Space and Astronautical Science, JAXA, Japan (3–1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252–5210, Japan) Erica R. Jawin Smithsonian Institution National Museum of Natural History, Department of Mineral Sciences, PO Box 37012, Washington, DC 20013–7012, USA Lauren M. Jozwiak Johns Hopkins Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD 20723, USA Chunlai Li Key Laboratory for Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, China Jianzhong Liu Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China Tomokatsu Morota Department of Earth and Planetary Science, University of Tokyo, Bunkyō-ku, Tokyo, Japan Debra H. Needham National Aeronautics and Space Administration Headquarters, Washington, D.C. 20546, USA Lillian R. Ostrach US Geological Survey Astrogeology Science Center, 2255 N. Gemini Drive, Flagstaff, AZ USA Carle M. Pieters Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA Tabb C. Prissel Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX 77058 USA Yuqi Qian Planetary Science Institute, China University of Geosciences, Wuhan, 430074, China Le Qiao Institute of Space Science, Shandong University, Weihai, 264209, China Malcolm R. Rutherford Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA David R. Scott Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA Jennifer L. Whitten Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA 70118 USA Long Xiao Planetary Science Institute, China University of Geosciences, Wuhan, 430074, China Feng Zhang National Space Science Center, No. 1 Nanertiao, Zhongguancun, Haidian District, Beijing, China Ouyang Ziyuan Key Laboratory for Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, China Publisher: Mineralogical Society of America First Online: 04 Dec 2023 Copyright © 2023 by the Mineralogical Society of AmericaMineralogical Society of America Reviews in Mineralogy and Geochemistry (2023) 89 (1): 453–507. https://doi.org/10.2138/rmg.2023.89.11 Article history First Online: 04 Dec 2023 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation James W. Head, Lionel Wilson, Harald Hiesinger, Carolyn van der Bogert, Yuan Chen, James L. Dickson, Lisa R. Gaddis, Junichi Haruyama, Erica R. Jawin, Lauren M. Jozwiak, Chunlai Li, Jianzhong Liu, Tomokatsu Morota, Debra H. Needham, Lillian R. Ostrach, Carle M. Pieters, Tabb C. Prissel, Yuqi Qian, Le Qiao, Malcolm R. Rutherford, David R. Scott, Jennifer L. Whitten, Long Xiao, Feng Zhang, Ouyang Ziyuan; Lunar Mare Basaltic Volcanism: Volcanic Features and Emplacement Processes. Reviews in Mineralogy and Geochemistry 2023;; 89 (1): 453–507. doi: https://doi.org/10.2138/rmg.2023.89.11 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Volcanism is a fundamental process in the geological evolution of the Moon, providing clues to the composition and structure of the mantle, the location and duration of interior melting, the nature of convection and lunar thermal evolution. Progress in understanding volcanism has been remarkable in the short 60-year span of the Space Age. Before Sputnik 1 in 1957, the lunar farside was unknown, the origin of the dark lunar maria was debated (sedimentary or volcanic), and significant controversy surrounded the question of how the multitude of craters on the surface formed. 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Channel-like forms are ubiquitous on steep hillslopes on Earth, Mars, and other planetary bodies. On Earth and Mars, these landforms are commonly attributed to water activity, especially for slopes below the angle of repose (similar to 30 degrees) where dry granular flows are considered ineffective. While the angle of repose characterizes loose sediment stability, it is unclear whether dry rockfall can traverse and erode channels in bedrock or cemented substrates. We used a large-scale experiment to show that bedrock chutes can form spontaneously at low gradients from dry rockfall. Our results, combined with observations of rocky outcrops and boulders on Mars, indicate that rockfall can be an important bedrock degradation process that can produce low-gradient channels in the absence of water.

Soil salt deliquescence and soil porewater solution growth are key processes that generate potentially habitable conditions in hyperarid environments on Earth and could form near-surface pore waters on Mars. However, direct detection of soils darkened by saline porewater solutions on Mars has proven difficult owing to the limited number of imaging opportunities over potential brine-bearing sites, the limited diel temporal coverage of orbital sensors, and the diversity of spectroscopic properties of potentially brine-bearing substrates that limits direct detection of hydrated mineral phases. Here, we explore how these observational limitations would affect the interpretation of highly dynamic soil salt patches observed in the McMurdo Dry Valleys, Antarctica. These salt patches show daily and seasonal albedo change, darkening and brightening over timescales of minutes. Fully darkened conditions occur at a median surface relative humidity of 67.9 & nbsp;+/- 10.7%, while bright conditions occur at lower median surface relative humidity of 38.9 & nbsp;+/- 14.5%, leading to the interpretation that the albedo changes are caused by soil salt deliquescence and brine droplet growth. These humidity thresholds and the daily hysteresis between deliquesced and effloresced conditions are consistent with the properties of sulfate and chloride salts found at the site, but occur on timescales much faster than those observed under laboratory conditions (minutes vs. hours-days). Darkened soil patch conditions are most common between 21:00 and 06:00 local time, and are not detected during 78% of afternoon imaging opportunities, suggesting that episodic, afternoon satellite imaging would not be effective in resolving rapid albedo changes on similar planetary landscapes such as Mars. Instead, synoptic, high-cadence imaging is a more suitable remote sensing tool for evaluating albedo changes driven by surface salt deliquescence and efflorescence.

Selected in 2019 as a NASA SIMPLEx mission, Lunar Trailblazer is in implementation for flight system delivery at the end of 2022. The mission's goal is to understand the form, abundance, and distribution of water on the Moon and the lunar water cycle. Lunar Trailblazer also collects data of candidate landing sites to inform planning for future human and robotic exploration of the Moon and evaluate the potential for in situ resource utilization. Lunar Trailblazer's two science instruments, the High-resolution Volatiles and Minerals Moon Mapper (HVM3) and the Lunar Thermal Mapper (LTM) provide simultaneous high-resolution spectral imaging data to map OH/water, crustal composition, and thermophysical properties from a $100\pm 30$ km lunar polar orbit. The ∼210-kg flight system deploys from an ESPA Grande and utilizes a ∼1000 m/s $\Delta\mathrm{V}$ hydrazine chemical propulsion system, similar to that employed by GRAIL. Trailblazing elements include the novel state-of-the-art dataset collected at substantially reduced price point, fully geographically co-registered data products delivered to the Planetary Data System, planetary mission team demographics, Caltech campus mission operations, and student staffing of select mission ops roles. Lunar Trailblazer's pioneering development is providing key lessons learned for future planetary small spacecraft.

Steep channel-like landforms-referred to here as bedrock chutes-line the rocky walls of some craters on the Moon and Mars. The role of volatiles, such as H2O or CO2, or dry rockfall in the formation of bedrock chutes is unknown on either planetary body. To test whether bedrock chute formation on Mars involved volatile activity, we used digital elevation models of Mars generated from HiRISE and CTX stereo-imagery to survey 4-9 km diameter craters globally and measure chute morphology as a function of latitude and orientation-properties that might co-vary with volatile activity. We also analyzed bedrock chutes on the Moon, which is presumably devoid of significant erosion due to volatile activity, using LROC NAC data, to serve as a volatile-free endmember for comparison with Mars. Martian bedrock chutes occur at all latitudes and have median values of chute spacing (wavelength) of similar to 300 m, relief of similar to 15 m, and slope of similar to 33 degrees. Chutes on the Moon are less common and are generally steeper (similar to 41 degrees) with less relief (similar to 5 m) as compared to Mars. While dry rockfall might have formed bedrock chutes on both the Moon and Mars, martian chutes are systematically deeper on pole-facing slopes between 10 degrees S-30 degrees S indicating a likely role for volatile activity in chute formation. Bedrock chutes are also deeper where they co-occur with well-incised martian gully channels. The latitude-dependence for deeper bedrock chutes on pole-facing slopes extends to lower latitudes than gullies-within the contemporary tropics-indicating the potential for volatile-related activity closer to the equator than documented for gullies or other ice-related features on Mars. Chutes carved into bedrock likely form slowly compared to gully channels, which are incised into more erodible ice-cemented sediment, and therefore might provide a longer record of environmental conditions over larger swaths of Mars.

The South Fork of Wright Valley contains one of the largest rock glaciers in the McMurdo Dry Valleys, Antarctica, stretching 7 km from the eastern boundary of the Labyrinth and terminating at Don Juan Pond (DJP). Here, we use results from ground-penetrating radar (GPR), qualitative field observations, soil leaching analyses and X-ray diffraction analyses to investigate rock glacier development. The absence of significant clean ice in GPR data, paired with observations of talus and interstitial ice influx from the valley walls, support rock glacier formation via talus accumulation. A quartz-dominated subsurface composition and discontinuous, well-developed desert pavements suggest initial rock glacier formation occurred before the late Quaternary. Major ion data from soil leaching analyses show higher salt concentrations in the rock glacier and talus samples that are close to hypersaline DJP. These observations suggest that DJP acts as a local salt source to the rock glacier, as well as the surrounding talus slopes that host water track systems that deliver solutes back into the lake, suggesting a local feedback system. Finally, the lack of lacustrine sedimentation on the rock glacier is inconsistent with the advance of a glacially dammed lake into South Fork during the Last Glacial Maximum.

The geomorphic record indicates that alpine glaciers in the McMurdo Dry Valleys of southern Victoria Land, Antarctica, appear to advance during interglacial periods in response to ice-free conditions in the Ross Sea. Few records of these advances are preserved and/or subaerially exposed, complicating the interpretations of regional glacier response to climate changes. Here, we present geophysical and geochemical analyses of a rock glacier that originates from icefalls fed by alpine Doran Glacier in central Taylor Valley. The rock glacier exhibits a trend of increased weathering of granitic clasts via ventifaction and grussification down-flow. Meltwater ponds on the rock glacier exhibit variable salinity that ranges from freshwater to higher than seawater, with the highest salinity pond near the rock glacier toe. Ground-penetrating radar analyses reveal the feature to possess a primarily clean ice interior, with layers of englacial debris. Stable isotopic data from three ice cores support a glacial origin for the ice within the rock glacier. These data suggest that the current morphology of the rock glacier is the result of multiple events of increased ice contribution caused by advances of Doran Glacier, which is the main source of ice to the rock glacier. We therefore demonstrate the potential of ice-cored rock glaciers to record multiple advances and retreats of Dry Valley glaciers, permitting the interpretation of glacial responses to Pleistocene and Holocene climate change even where direct records are not present.

Abstract We report on a decade of fieldwork designed to determine the conditions required for erosion of Mars-like gully channels in the McMurdo Dry Valleys (MDV) of Antarctica. We have outlined the major factors in the morphological evolution of gullies in the Inland Mixed Zone of the MDV: (1) the distribution of ice sources; (2) the temporal aspects of ice melting; and (3) the relative significance of melting events in gullies. We show that significant erosion of gully channels can be achieved if geometrical and environmental conditions combine to concentrate ice where it can rapidly melt. In contrast, annual melting of surface ice and snow deposits during late-season discharge events contribute to transport of water, but flux rarely surpasses the infiltration capacity of the active layer. These small discharge events do not erode channels of significant width. Even when the flux is sufficient to carve a c. 10–20 cm deep channel during late summer (January–February) runoff, these small channels seldom persist through multiple seasons, because they are seasonally muted and filled with aeolian deposits. We briefly discuss the application of these results to the study of gully systems on Mars.

Polygonal ridge networks, also known as boxwork or reticulate ridges, are found in numerous locations and geological contexts across Mars. Distinguishing the morphologies and geological context of the ridge networks sheds light on their potential as astrobiological and mineral resource sites of interest. The most widespread type of ridge morphology is characteristic of the Nili Fossae and Nilosyrtis region and consists of thin, criss-crossing ridges with a variety of heights, widths, and intersection angles. They are found in ancient Noachian terrains at a variety of altitudes (between -2500 and 2200 m) and geographic locations and are likely to be chemically altered fracture planes or mineral veins. They occur in the same general areas as valley networks and ancient lake basins, but they are not more numerous where these water-related features are concentrated, and can appear in places where th morphologies are absent. Similarly, some of the ridge networks are located near hydrated mineral detections, but there is not a one-to-one correlation. Smaller, light-toned ridges of variable widths have been found in Gale Crater and other rover sites and are interpreted to be smaller versions of the Nili-like ridges, mostly formed by the mineralization of fractures. This type of ridge is likely to be found in many other places on Mars as more high-resolution data become available. Sinus Meridiani contains many flat-topped ridges arranged into quasi-circular patterns. The ridges are eroding from a clay-rich unit, and could be formed by a similar process as the Nili-type ridges, but at a much larger scale and controlled by fractures made through a different process. Hellas Basin is host to a fourth type of ridge morphology consisting of large, thick, light-toned ridges forming regular polygons at several superimposed scales. While still enigmatic, these are most likely to be the result of sediment-filled fractures. The Eastern Medusae Fossae Formation contains large swaths of a fifth, previously undocumented, ridge network type. The dark ridges, reaching up to 50m in height, enclose regular polygons and erode into dark boulders. These ridge networks are interpreted to form as a result of lava flow embayment of deeply fractured Medusae Fossae Formation outcrops. (C) 2016 Published by Elsevier Inc.

Reconstructions of the orbital parameters of Mars spanning the last similar to 20 Myr, combined with global circulation models, predict multiple cycles of accumulation and degradation of an ice-rich mantle in the mid-latitudes, driven primarily by insolation at the poles during periods when obliquity was more than ten degrees greater than it is today (i.e., >similar to 35 degrees). While evidence of an ice-rich "latitude dependent mantle" (LDM) consistent with these predictions is abundant, features indicative of cycles of emplacement and degradation of this unit are isolated and rare. In addition, fundamental physical properties of the LDM, such as paleo-thickness maxima, have not been determined. Gullies, which are sinuous channels found on steep slopes in mid- and high-latitudes, interact with the LDM and provide a stratigraphic feature useful for documenting both cyclical emplacement/removal and thickness estimates in past climate regimes. In the southern hemisphere, where gullies are most common, we present extensive evidence of (1) cyclical degradation and removal of gullies in the lower mid-latitudes (30-40 degrees S), and (2) burial and exhumation of inverted gully channels in the transitional latitude band between dissected and preserved LDM (40-50 degrees S), which can only be accounted for if an additional tens of meters of LDM were present at these locations during channel formation. These relationships support a model in which end-to-end gully evolution is controlled by the behavior of the LDM: at lower latitudes, gullies incise an ice-rich substrate and are removed when that ice becomes unstable, and at higher latitudes gullies are buried by successive emplacement of LDM where ice remains stable near the surface. Further, the presence of dormant buried gullies implies that present-day activity within gullies, likely to be controlled by the behavior of CO2 frost, is insufficient to explain the entire gully population, and that conditions conducive to increased gully activity preceded the most recent phase of LDM emplacement. (C) 2015 Elsevier Inc. All rights reserved.

Although the drivers of climate change and its consequences in polar regions are becoming better understood [Holland and Bitz, 2003] and well monitored [Serreze et al., 2002; Doran et al., 2002b], measuring the responses of polar landscapes to changing climate boundary conditions is challenging: Polar landscapes typically respond slowly to warming but abruptly to melting [Gooseff et al., 2011].

Mars is the only planet other than Earth in the Solar System that has a preserved nonpolar geological record of glaciation on its surface. Nonpolar ice deposits on Mars have been linked to variations in spin-axis obliquity that cause mobilization of polar ice and redeposition at lower latitudes, forming ice-rich and glacial deposits. Remnant nonpolar glacial deposits are found across the northern mid-latitudes where surface ice is not currently stable, implying that different climatic conditions existed on Mars in the past. Individual glacial deposits are often too small to date reliably using impact crater size-frequency data. We describe a novel approach that allows us to derive new information about when glaciation occurred in broad areas of the northern mid-latitudes. In this region we have classified (1) craters that superpose preexisting glacial deposits and were modified by later accumulation (and therefore formed during an epoch when glaciation was occurring), and (2) craters that are superposed on glacial deposits but are themselves unmodified by ice accumulation (and thus post-date significant glaciation). The sparse population of post-glacial craters reveals that the last period of extensive ice deposition of this type in this latitude band was recent (Late Amazonian). The substantial number of craters formed during the recurring glacial periods implies that northern mid-latitude glaciation was a long-lived recurring process, occurring over a period of at least similar to 600 m.y. On the basis of Mars atmospheric general circulation models, these results are consistent with higher obliquity being common in the past, with recurring periods of obliquity exceeding the 25 degrees axial tilt of Mars today. These observations support the statistical prediction of J. Laskar and colleagues that the median obliquity during the Amazonian was similar to 35-40 degrees.

The discovery on Mars of recurring slope lineae (RSL), thought to represent seasonal brines, has sparked interest in analogous environments on Earth. We report on new studies of Don Juan Pond (DJP), which exists at the upper limit of ephemeral water in the McMurdo Dry Valleys (MDV) of Antarctica, and is adjacent to several steep-sloped water tracks, the closest analog for RSL. The source of DJP has been interpreted to be deep groundwater. We present time-lapse data and meteorological measurements that confirm deliquescence within the DJP watershed and show that this, together with small amounts of meltwater, are capable of generating brines that control summertime water levels. Groundwater input was not observed. In addition to providing an analog for RSL formation, CaCl2 brines and chloride deposits in basins may provide clues to the origin of ancient chloride deposits on Mars dating from the transition period from "warm/wet" to "cold/dry" climates.

Thermokarst is a land surface lowered and disrupted by melting ground ice. Thermokarst is a major driver of landscape change in the Arctic, but has been considered to be a minor process in Antarctica. Here, we use ground-based and airborne LiDAR coupled with timelapse imaging and meteorological data to show that 1) thermokarst formation has accelerated in Garwood Valley, Antarctica; 2) the rate of thermokarst erosion is presently ~ 10 times the average Holocene rate; and 3) the increased rate of thermokarst formation is driven most strongly by increasing insolation and sediment/albedo feedbacks. This suggests that sediment enhancement of insolation-driven melting may act similarly to expected increases in Antarctic air temperature (presently occurring along the Antarctic Peninsula), and may serve as a leading indicator of imminent landscape change in Antarctica that will generate thermokarst landforms similar to those in Arctic periglacial terrains.